Herpesviruses are amongst the largest, most complex and most variable of all DNA viruses. There are some common laboratory strains which have provided valuable information on the biology of the viruses. However, there are behavioral differences between laboratory strains and clinical isolates and even within the different clinical isolates themselves. It has been difficult to understand how these differences are manifested in virulence and pathogenicity. In this application, synthetic biology methods will be used to first build an infectious clone of the herpes simplex virus type 1 (HSV-1) genome and then show the utility and versatility of this genome engineering method by creating chimeras between a clinical isolate and a laboratory strain to more easily determine the functional consequences of the clinical strain differences. The successful outcome of this synthetic biology approach would have a significant impact on the ability to synthetically clone and manipulate any herpesvirus genome or large virus. This, in turn, will enable the larger research community to better understand the biology of viruses. In addition, this approach offers a paradigm to help understand the biology of emerging viruses.